Despite recent progress in its prevention, the Sudden Infant Death Syndrome (SIDS) remains the most frequent cause of infant mortality between the ages of one month and one year in the United States. A striking epidemiological finding is that more victims than expected are found in the prone position, often with the face in the bedclothes. Campaigns to encourage putting infants to sleep on their backs have led to a gratifying reduction in the incidence of SIDS in several countries, yet the influence of posture remains mysterious. This project will use decerebrate neonatal piglets to explore the possibility that the risk of prone sleeping is determined by reflex responses involving the upper airway, and that these responses may be aggravated by CO2 in the upper airway (from re-breathing), by abnormalities of the ventral medulla (for which there is evidence in some SIDS victims), or from elevated body temperature (for which there is epidemiologic evidence and an intriguing report of a study in puppies). We will examine the influence of each of these conditions on three upper airway reflex responses: the "diving" response, the laryngeal chemo reflex and the load-compensating reflex response to upper airway obstruction. Our general hypothesis is that some combination of conditions and stimuli will exaggerate the reflex interruption of breathing, possibly contributing to the pathogenesis of SIDS. [unreadable] [unreadable]